1. Field of the Invention
The present invention relates to a workpiece composite including a preform and a gel.
2. Description of Related Art
Workpiece composites containing a preform and a gel, which is accommodated in a recess of the preform, are used as pressure sensors, for example. The preform may contain a pressed screen of a printed circuit board, for example, and may be connected to a pressure sensor chip. The pressure sensor chip is positioned over a recess in the preform. The gel fills the recess and the area underneath the diaphragm of the pressure measuring chip. In general, the pressure measuring chip is bonded to the preform with the aid of an accessory agent.
Normally the gel is a passivating gel which is used as a barrier against harmful media. These are, for example, corrosive media.
However, unhardened passivating gels usually tend to creep. It is necessary to select the time period between the application of the gel and hardening to be as short as possible in order to limit areas affected by creeping to a minimum. Another option for preventing creeping is the formation of edges at which creeping stops. However, these edges may stop creeping only temporarily.
In order to prevent oils from creeping on surfaces, i.e., to prevent a surface from being wetted by an oil, it is known, for example, from published German patent document DE A 196 49 955, to coat a substrate with a fluoroalkyl-functional organopolysiloxane-containing composition. Coatings of this type are offered commercially, for example, by the Dr. Tillwich Company. Published German patent document DE A 198 47 303 describes a sensor element having an anti-adhesive surface coating. The surface coating has a compound selected from the group of the fluoropolymers, fluorormocers, polymeric fluorocarbon resins, fluorine-containing silanes, or partially fluorinated polymers.